The present invention relates to a sulfur transfer additive for catalytic cracking of hydrocarbons and a catalytic cracking process of hydrocarbons. More particularly, the present invention relates to a liquid sulfur transfer additive for catalytic cracking of hydrocarbons comprising at least two metal elements, and a catalytic cracking process using said sulfur transfer additive.
The hydrocarbon feed processed in the commercial fluidized catalytic cracker (FCC) usually contains 0.3 to 3.0% by weight of sulfur. Based on the total amount of the sulfur contained in the hydrocarbon feed, about 20 to 60% by weight of the sulfur is transferred to the cracked gas in form of H2S, which can be recovered by converting it into elemental sulfur, about 20 to 70% by weight to the light oil products as organic sulfur compounds, which must be removed from the oil products by means of hydrotreating or hydrofining, and the remaining about 5 to 30% by weight to the coke deposited on the catalyst particles. However, when the amount of sulfur contained in the hydrocarbon feed is higher, the light oil products will contain too much of sulfur to meet the standard specifications for the products. Although the sulfur content in the light oil products can be reduced to meet the specifications by lowering the initial boiling point (IBP) or by means of other more severe post-treatment, this will increase the costs and decrease the profits. In the catalyst regenerator of the FCC system, the sulfur contained in the coke is burned off, forming sulfur dioxide and sulfur trioxide (collectively called SOx hereinafter), which are emitted to the atmosphere with the flue gas, resulting in environmental pollution. In addition, the higher amount of SOx in the regenerator flue gas leads to corrosion of the regenerator equipment.
The solution most widely used nowadays to reduce the SOx content in regenerator flue gas and the sulfur content in light oil products of FCC system is the use of solid sulfur transfer additives. The solid sulfur transfer additives can be divided into two categories. One is the additives dedicated to reduce the SOx concentration in regenerator flue gas, and the other is the additives dedicated to reduce the sulfur content in light oil products, especially gasoline. The sulfur transfer additives described in U.S. Pat. Nos. 4,589,978 and 5,021,228 fall into the first category, while the sulfur transfer additive described in U.S. Pat. No. 5,376,608 falls into the second category. The sulfur transfer additive disclosed in U.S. Pat. No. 4, 589, 978 contains 1xcx9c20% of lanthanum (La), cerium (Ce) and a support, wherein the weigh ratio of lanthanum to cerium is 1:10 to 10:1, and the support can be alumina, silica, kieselguhr or zeolite, etc. This sulfur transfer additive is used as separate particles and mixed with the catalytic cracking catalyst. With this sulfur transfer additive, it is required to operate the regenerator at a full CO combustion mode, 0-2% (vol.) excess of O2. When 0.5xcx9c4.8% of the sulfur transfer additive based on the catalyst inventory of the FCC system is added, SOx can be reduced by 30xcx9c80%. U.S. Pat. No. 5,021,228 disclosed a sulfur transfer additive which is a composition containing (1) porous alumina support, (2) as a first component the metals of actinium series such as the thorium and uranium in amount of 0.5xcx9c10 wt. %, (3) as a second component the alkali metal such as potassium and sodium in amount of 1xcx9c5% wt. %. This composition is used as one component of the catalytic cracking catalyst and 60% of SOx can be transferred to H2S. U.S. Pat. No. 5,376,608 disclosed a catalytic cracking catalyst composition comprising a zeolite dispersed in an inorganic oxide matrix and, as a separate component, a Lewis acid supported on alumina, wherein the separate component comprises 1xcx9c50 wt. % of elements and compounds Ni, Cu, Zn, Ag, Cd, Ti, Bi, B and Al. Other components of the composition are 5xcx9c50 wt. % of synthetic faujasite, 10xcx9c60 wt. % of clay, and 10xcx9c30 wt. % of inorganic binder selected from silica, alumina and silica-alumina. It was reported that the sulfur content in gasoline was markedly reduced without any negative effect on the gasoline yield using the composition.
The prior art sulfur transfer additives such as those disclosed in the above-mentioned patents are of only single-function, i.e. the additives which can reduce the SOx concentration in regenerator flue gas can not reduce the sulfur content in the light oil products, and the additives which can reduce the sulfur content in the light oil products can not reduce the SOx concentration in regenerator flue gas. Furthermore, these sulfur transfer additives have no catalytic activity, and will dilute the catalyst if added into the cracking catalyst. As a result, the activity of the catalyst in the FCC system is reduced and the selectivity becomes deteriorated. For instance, when 5.0% of sulfur transfer additive is added to an equilibrium catalyst with a microactivity of 60, the microactivity will be lowered by about 3 unit and the selectivity is significantly affected. Additionally, the prior art sulfur transfer additives are all solid, thus requires that the particle distribution, mechanical strength and sphericity of the sulfur transfer additives be matched well with those of the catalyst. When the solid particles are added to the FCC system, the ratio of the su transfer additive to the catalyst inventory in the system can not be flexibly adjusted, thus, can not accommodate to the operation for frequent variations in the sulfur content in the hydrocarbon feed. Furthermore, the preparation of the solid sulfur transfer additives need complex equipment.
It is an object of the present invention to provide a liquid sulfur transfer additive and a catalytic cracking process using the same, which can reduce the SOx content in the regenerator flue gas and the sulfur content in the light oil products at the same time, and has no negative effect on the activity and selectivity of the catalyst in FCC system, so as to overcome the defects of the prior art solid sulfur transfer additives i.e. the solid sulfur transfer additives in the prior art can only reduce the SOx content in the regenerator flue gas or can only reduce the sulfur content in the light oil products, and to obviate the negative effect of the prior art sulfur transfer additives on the cracking catalyst activity and selectivity, After extensive and profound research, the present inventors find the following sulfur transfer additive and catalytic cracking process, and achieve the object as stated above.
In the first aspect, the present invention provides a sulfur transfer additive for catalytic cracking of hydrocarbons, characterized in that it is a liquid product comprising at least two metal elements selected from the following three classes:
a). alkali earth metals,
b). transition metals and P zone metals, and
c). rare earth metals,
and wherein there are at least two metal elements from the different classes.
In the second aspect, the present invention provides a process for catalytic cracking of hydrocarbons, characterized in that the sulfur transfer additive as stated in the first aspect of the present invention is used.
In yet another aspect, the present invention provides an application process of the sulfur transfer additive of the present invention as stated above.
These and other aspects of the present invention are apparent to the ordinary skilled in the art with reference to the following detailed description of the present invention.
The sulfur transfer additive of the present invention comprises at least two metal elements selected from the following three classes: a) alkali earth metals, b) transition metals and P zone metals, and c) rare earth metals, and wherein there are at least two metal elements from the different classes. That is to say, the present sulfur transfer additive comprises at least one metal element selected from alkali earth metals and at least one metal element selected from transition metals and P zone metals, or comprises at least one metal element selected from alkali earth metals and at least one metal element selected from rare earth metals, or comprises at least one metal element selected from transition metals and P zone metals and at least one metal element selected from rare earth metals, or comprises at least one metal element selected from alkali earth metals, at least one metal element selected from transition metals and P zone metals and at least one metal element selected from rare earth metals.
In the present application, the term xe2x80x9calkali earth metalsxe2x80x9d refers to Group IIA metal elements in the Mendelyeev Periodic Table of Elements, and includes Be, Mg, Ca, Sr, Ba and Ra, preferably Mg, Ca, Sr and Ba, and more preferably Mg and Ca. The term xe2x80x9ctransition metalsxe2x80x9d refers to the metal elements of Group IB to VIIB and Group VIII in the Mendelyeev Periodic Table of Elements excluding Lanthanide series elements and Actinium series elements, preferably Sc, Ti, Zr, Hf, V, Cr, Mn, Fe, Co, Ni, Pd, Cu, Ag, Zn, Cd and the like, more preferably Zn, Ag, Cd and Ti. The term xe2x80x9cP zone metalsxe2x80x9d refers to the metal and metalloid elements in P zone, i.e. Group IIIA to VIIA in the Mendelyeev Periodic Table of Elements, and includes B, Al, Ga, In, Ti, Si, Ge, Sn, Pb, P, As, Sb, Bi, Te and Po, preferably B, Al, Ga, In, Ge, Sn, Pb, Sb and Bi, and more preferably B, Al, Ga, Sn, Pb and Bi, and most preferably Bi, Al, Pb and Sn. The term xe2x80x9crare earth metalsxe2x80x9d refers to the Lanthanide series elements in the Mendelyeev Periodic Table of Elements, and includes the elements with atomic number of from 57 to 71, preferably La, Ce, Pr, Nd, Pm, Sm, Eu and Gd, more preferably La, Ce, Pr and Nd.
The metal elements in the present sulfur transfer additive can be present in any compound form, such as oxide, hydroxide, organic acid salt, inorganic acid salt, complex or the like of the metal elements. The selection on the specific metal compound depends upon the solubility, emulsifiability or dispersability of the compound in the relevant liquid medium (solvent, emulsifying medium, suspending medium or dispersing medium), to facilitate the formulation of the present liquid sulfur transfer additive in form of a solution, colloid, emulsion, suspension or dispersion etc. The metal elements are preferably present in the present sulfur transfer additive as organic acid salts or inorganic acid salts. When the metal elements are present as organic acid salts, the organic acid can be, for example, substituted or unsubstituted, saturated or unsaturated carboxylic acid, alkyl- or aryl-sulfonic acid, any combination thereof, or the like. The specific example thereof includes propanoic acid, malonic acid, butanoic acid, isobutyric acid, 2-methyl butanoic acid, octanoic acid, isooctanoic acid, isononanoic acid, benzoic acid, naphthenic acid, citric acid, tartaric acid, fatty acid, oleic acid, dodecylbenzene sulfonic acid, para-toluene sulfonic acid and the like. When the metal elements are present as inorganic acid salts, the inorganic acid can be, for example, nitric acid, phosphoric acid, sulfonic acid, carbonic acid, sulfuric acid, chlorhydric acid, hydrobromic acid and the like, preferably nitric acid, phosphoric acid, sulfonic acid and carbonic acid.
There is no particular restriction on the ratio among the metal elements in the present sulfur transfer additive, and the ratio can be varied depending upon, for example, the desired sulfur content in the light oil products and the desired Sox content in the regenerator flue gas. In general, if it is required to decrease the sulfur content in the light oil products to a much lower level, it is advantageous to increase the proportion of the metal elements of class b) and/or c); and if it is required to decrease the SOx content in the regenerator flue gas to a much lower level, it is desirable to increase the proportion of the metal elements of class a) and/or c) However, in the present sulfur transfer additive, the weight ratio of the metal elements of class a) to class b), or class a) to class c), or class b) to class c) is generally from 1:20 to 20:1, preferably from 4:16 to 16:4, and more preferably from 8:12 to 12:8.
As stated above, the present sulfur transfer additive is a uniform liquid product The term xe2x80x9ca uniform liquid productxe2x80x9d means that the compounds of said metal elements are uniformly distributed in a liquid medium, to form, for example, a solution, colloid, emulsion, suspension, dispersion or the like of the metal compounds. There is no particular restriction on the liquid medium used in the present sulfur transfer additive, and any liquid medium which can uniformly distribute the relevant metal compounds to form a solution, colloid, emulsion, suspension or dispersion can be used. The liquid medium can, for example, be water, alcohols, hydrocarbons, ethers, ketones, any combination thereof and the like. The specific example thereof includes water, methanol, ethanol, benzene, toluene, xylene, ethylbenzene, isooctane, dodecane, and 200# solvent oil, etc. If desired, for example to assist in dispersing, stabilizing, emulsifying and/or dissolving, an assistant component can be additionally used in the present sulfur transfer additive. The assistant component can be alcohols, ethers, esters, amines, amides, alcohol amines, ionic or non-ionic surfactants, any combination thereof, and the like. The specific example thereof includes ethylene glycol, propylene glycol, diethylene glycol, isobutanol, methyl isobutyl ether, ethylene glycol dimethyl ether, propylamine, butylamine, ethylenediamine, 1,4-butylenediamine, dimethyl formamide, benzoic amide, monoethanolamine, diglycolaine, polyvinyl alcohol, nonylphenol polyoxyethylene ether, aliphatic alcohol polyoxyethylene ether, oleic diethanolamide, etc., preferably ethylene glycol, diethylene glycol, methyl isobutyl ether, diglycolamine, nonylphenol polyoxyethylene ether, and oleic diethanolamide.
There is no particular restriction on concentration of the metal compounds, and amount of the liquid medium and optional assistant component in the present sulfur transfer additive, as long as a uniform liquid product, especially a stable solution, colloid, emulsion, suspension or dispersion can be formed. However, in an embodiment of the present invention, the present sulfur transfer additive is water-soluble, and contains, based on the total weight of the additive, 10 to 80%, preferably 15 to 70%, more preferably 25 to 60%, most preferably 35 to 50% by weight of the metal compounds, 10 to 50%, preferably 20 to 45%, more preferably 25 to 40%, most preferably 30 to 36% by weight of the liquid medium, and 10 to 40%, preferably 12 to 36%, more preferably 15 to 32%, most preferably 20 to 30% by weight of the assistant component. This water-soluble additive is low in costs, easy to be handled and cleaned, and less hazardous. In another embodiment of the present invention, the present sulfur transfer additive is oil-soluble, and contains, based on the total weight of the additive, 50 to 85%, preferably 53 to 80%, more preferably 57 to 75%, most preferably 60 to 70% by weight of the metal compounds, 10 to 30%, preferably 12 to 28%, more preferably 15 to 26%, most preferably 18 to 25% by weight of the liquid medium, and 5 to 20%, preferably 7 to 18%, more preferably 10 to 16%, most preferably 12 to 14% by weight of the assistant component. This oil-soluble additive is soluble in the FCC feed and can be well dispersed in hydrocarbons.
The present sulfur transfer additive can be easily prepared in a conventional manner. Based on the teachings of the present application, the uniform liquid product of the present invention can be prepared from the properly selected metal compounds, liquid medium and optional assistant component by various well-known means in the art to prepare a solution, colloid, emulsion, suspension or dispersion. For example, the present sulfur transfer additive in form of a solution, colloid, emulsion, suspension or dispersion can be prepared as follows: a specified amount of metal compounds, liquid medium and optional surfactant are mixed thoroughly at a certain temperature, the mixture is then made to be a uniform liquid by means of colloid mill, ultrasonic wave or the like, and if necessary, a small amount of assistant component is added while stirring, finally a stable liquid product is obtained. More specifically, an illustrative preparation method in laboratory is as follows: a certain amount of metal compounds, equal equivalent of organic or inorganic acid, and proper amount of liquid medium are added to a round-bottom flask. The mixture is heated at a reflux temperature of for example 100 to 130xc2x0 C. under stirring for a period, usually for 3 to 15 hours, preferably 5 to 10 hours. Then the contents in the flask is cooled down to for example 50 to 80xc2x0 C., a proper amount of assistant component is added, and the mixture is further stirred for a certain period such as 1 to 2 hours, to obtain a uniform liquid product.
In the second aspect, the present invention provides a process for catalytic cracking of hydrocarbons wherein the liquid sulfur transfer additive as described in the first aspect of the present invention is used to decrease the sulfur content in the light oil products and/or the SOx content in the regenerator flue gas. The present catalytic cracking process includes various types of fluidized catalytic cracking processes, for example, gas oil fluidized catalytic cracking, residuum catalytic cracking (RFCC), deep catalytic cracking (DCC), and other fluidized catalytic cracking derivative processes based on the continuous reaction-regeneration mechanism of fluidized catalytic cracking for processing hydrocarbons, such as MGG, ARGG, MIO and the like. Except the use of the present liquid sulfur transfer additive, the process parameters, equipment used and flow scheme of the present catalytic cracking process are the same as those in the prior art, and are well-known in the catalytic cracking art.
As the sulfur transfer additive used is a liquid product, the addition system for the additive needs no complex equipment, and can comprise only a tank, a pump and necessary pipes. In the present catalytic cracking process, the liquid sulfur transfer additive can be added into the reactor together with the catalytic cracking feed stream or together with the steam, or can be added into the reactor and/or regenerator separately as a separate stream. Additionally, the liquid sulfur transfer additive can be used together with other liquid process additive or stream, for example, it can be added into the reactor and/or regenerator after being mixed with metal passivator, or slurry antifoulant, or riser reactor quench oil. Said catalytic cracking feed stream can be fresh feedstock and/or recycled feed oil, i.e. recycled oil and recycled slurry.
In the present catalytic cracking process, the addition amount of the sulfur transfer additive can be varied over a wide range, and the specific addition amount depends upon several factors such as the specific operation conditions for the catalytic cracker, the-sulfur content in the feedstock, the desired SOx level in the flue gas, the desired sulfur content in the light oil products, and the concentration of the effective components (i.e. the metal compounds) in the sulfur transfer additive, etc. Taking the specific operation conditions and the various requirements into consideration, the ordinary skilled in the art can easily determine the addition amount of the sulfur transfer additive via routine experiments. In general, the sulfur transfer additive is added in such an amount that the deposit amount of the sulfur transfer additive on the catalyst is above 0 to 10%, preferably 0.05 to 6%, more preferably 0.1 to 4%, most preferably 0.2 to 1% by weight, said xe2x80x9cdeposit amountxe2x80x9d is the weight percent of the total weight of the metal elements provided by the sulfur transfer additive and deposited on the catalyst based on the weight of the catalyst in the FCC system.
The general and preferable selections with respect to the sulfur transfer additive in the first aspect of the present invention also apply to the present catalytic cracking process.
The liquid sulfur transfer additive and the catalytic cracking process provided by the present invention can reduce the SOx concentration in regenerator flue gas by 10xcx9c80% and the sulfur content in the light oil products by 5xcx9c30% without any negative effect on the activity and selectivity of the catalyst of FCC system. As the sulfur transfer additive is a liquid, the preparation thereof needs no complex equipment such as spray drying equipment, etc., and it can be manufactured at a lower cost, the addition amount of the liquid sulfur transfer additive can be flexibly adjusted, and thus, can be controlled automatically.
The following examples are provided to illustrate the present invention. The examples are not intended to limit the scope of the present invention in any way, and they should not be so interpreted.
In the present application, the microactivity of a catalyst is determined in the conventional test method well-known in the art using the following test conditions:
The microactivity (MA) is calculated according to the following equation:
MA=100xe2x88x92W1(100xe2x88x92G)/W
wherein W is the weight of the feedstock in grams, W1 is the weight of the converted oil products in grams, and G is the weight percent of the gas oil in the converted oil products.
In the following Example 7, the sulfur transfer performance of the present sulfur transfer additive is evaluated in a test on a fixed-bed plant, which is carried out as follows. 5 g of catalytic cracking catalyst aged and impregnated with the sulfur transfer additive is loaded to the reactor, is subject to SOx uptake for 1 hour in atmosphere of a reaction gas consisting of SO2, N2 and O2 at a temperature of 730xc2x0 C., then is stripped with N2 for 10 minutes and finally is desorbed with a reducing gas consisting of H2 and H2O at a temperature of 520xc2x0 C. The SOx removal rate can be calculated according to the following equation.
SOx removal rate (v%)=(SO2% in the initial reaction gas SO2% after SOx uptake by the catalyst)/SO2% in the initial reaction gas